The present invention is directed to a rotary air coupling that provides a means to distribute air from an air supply to vehicle tires mounted on a rotating hub of a vehicle drive axle.
Automatic tire inflation systems (ATIS) are becoming popular with the trucking industry. Various types of ATIS systems have been developed, both for trailer axles and tractor drive axles. Existing air distribution systems for tire inflation systems on drive axles direct the supply air through the bearings of the hub. Distribution through the bearings demand smaller bearings and require additional seals in the hub. The seal life is shortened due to the increased seal friction caused by pressure loading of the seal lips.
The present invention is particularly directed to a rotary air coupling designed to distribute supply air to the tires mounted on drive axles in which the air coupling is positioned externally of the drive axle and the hub bearings. Therefore, the improved rotary air coupling of the present invention by being mounted outside the bearings of the hub have no effect on existing hub bearings.
However, a rotary air coupling, which includes a stationary seal and a rotating seal must be accurately positioned relative to each other and therefore requires small tolerances, such as five to ten thousands of an inch. Generally, the tolerances in wheel assemblies on an axially driven truck are quite large and thus are not suitable mounting surfaces. However, one set of surfaces in a wheel assembly that are tightly controlled is the relationship between the brake shoes and the brake drum. The present improved rotary air coupling takes advantage of this controlled dimension by connecting the stationary component of the coupling to the brake mounting plate directly or through the axle housing, while the rotary component of the coupling is connected to the hub and thus to the brake drum, such as by being attached to the wheel lugs of the hub.
One of the advantages of the present invention is that the rotary coupling of the present invention does not interfere with the drive axle, bearings or lubrications as internal axle type air couplings can. Thus, there is no interference in the strength of existing vehicle components which can lead to lengthy testing delays demanding by OEMs. Another advantage is the accessibility of the present rotary coupling. The present rotary coupling can be accessed as easily as brake shoes and will not cause mechanical difficulty in reassembly.